1. Field of the Invention
This invention relates to apparatus for actuating a safety device, and more particularly for actuating a door release arrangement on a device for holding open doors such as fire doors in the event of a fire alarm being raised. Such a holding device is referred to herein as a "door holder". The invention also relates to apparatus for releasing or closing a closure (such as a door).
2. Related Art
Door holders are available in several forms. A simple hook and eye is most popular, with other devices using friction between the floor and a rubbing surface. There are magnetic types available which consist of two parts with attracting polarities, one being fixed to the door and the other to an adjacent surface.
Some such magnetic types are electromagnetic with the supply current being connected via an appropriate fire alarm system. The door release arrangement is hard-wired into the system in such a way that it acts to cut the electric supply to the electromagnet on activation of the fire alarm. Hence the door is allowed to close and thus form part of a safety fire break.
Electromagnetic door holders including such a door release arrangement are, however, expensive and complicated to fit, especially retrospectively. Consequently many fire doors are permanently held open with any suitable object that may be to hand. This is often, ironically, a fire extinguisher.
It is known from U.S. Pat. No. 4,520,503 to provide a tone discrimination circuit for use with audible smoke or fire detectors or similar audible devices, which automatically emits an output electronic alarm signal, for notification of persons at remote locations, upon input of a proper audio tone from the smoke detector or other audible device. The circuit contains in series a microphone, a two stage audio amplifier, a frequency detector, and a tone discrimination circuit. The circuit emits an output electronic alarm signal if and only if the audio input signal has sufficient amplitude, the desired frequency, and the desired duration.